Electroconductive structure and electroplating method using the structure

ABSTRACT

A structure that is endowed with electric conductivity by plate-coating with a titanium nitride layer or by generation of a titanium nitride layer on a surface of a base material made of an inorganic material or an organic material, and a method of electroplating a cathode with a simple metal or an alloy, wherein the structure is used as an anode and/or a cathode. The structure is corrosion-resistant and has high electroconductivity, and thus the electroplating method using the structure allows the simplification and the cost reduction of an electroplating process.

TECHNICAL FIELD

[0001] The present invention relates to a structure having on its basematerial surface a specific compound layer and having electricconductivity, and to an electroplating method using the structure.

BACKGROUND ART

[0002] Since platinum is superior in corrosion resistance, platinum iswidely used for electrodes, plating, ornaments and others. At present,however, platinum is more expensive than other metals such as gold.Thus, it has been desired to supply electrodes, plating, ornaments andothers using other relatively inexpensive metals.

[0003] Japanese Patent Application Laid-Open Gazette (JP-A) No. 7-18469(laid-open date: Jan. 20, 1995) discloses a golden plated ornamenthaving, as its topmost surface, a gold alloy coated layer. JapanesePatent-Application Publication Gazette (JP-B) No. 6-39684 (publicationdate: May 25, 1994) also discloses an ornament plated with a simplemetal such as gold, or an alloy.

[0004] However, both plating treatments with gold, which are used inthese prior techniques, are dry plating treatments and are notelectroplating treatments using electrolysis.

[0005] In plating process of titanium with gold, it is necessary to usetwo-stages process in which titanium is plated with nickel and thenplated with gold. Thus, it has been desired to make the process simpler.

[0006] An object of the present invention is to provide a structure thatis inexpensive and has corrosion resistance and electric conductivity,and provide an inexpensive electroplating method the process of which issimple.

DISCLOSURE OF INVENTION

[0007] The present inventor has paid attention to the matter thattitanium nitride (TiN) is a good conductor for electricity, and hasfound out that a structure having a titanium nitride layer has goodelectric conductivity and this structure is used to carry out anelectroplating method, whereby an electroplated product can beinexpensively obtained through a simple process. Thus, the presentinvention has been made.

[0008] That is, the present invention relates to a structure that isendowed with electric conductivity by plate-coating with a titaniumnitride layer or by generation of a titanium nitride layer on a surfaceof a base material made of an inorganic material.

[0009] The present invention also relates to a structure that is endowedwith electric conductivity by plate-coating with a titanium nitridelayer or by generation of a titanium nitride layer on a surface of abase material made of an organic material.

[0010] The base material may be made of a metal having electricconductivity. In particular, the base material may be made of titaniumor a titanium alloy. In this case, the base material surface issubjected to direct nitriding, whereby a structure endowed with electricconductivity can be obtained. The base material may be made of amaterial having no electric conductivity.

[0011] The thickness of the titanium nitride layer may be from 0.01 to 3μm.

[0012] The present invention relates to a method of electroplating acathode with a simple metal or an alloy, wherein an anode comprises astructure that is endowed with electric conductivity by plate-coatingwith a titanium nitride layer or by generation of a titanium nitridelayer on a surface of a base material made of an inorganic material oran organic material.

[0013] Furthermore, the present invention relates to a method ofelectroplating a cathode with a simple metal or an alloy, wherein thecathode comprises a structure that is endowed with electric conductivityby plate-coating with a titanium nitride layer or by generation of atitanium nitride layer on a surface of a base material made of aninorganic material or an organic material.

[0014] In the above-mentioned methods, the cathode can be plated with anoble metal.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The ingredient of the base material is not particularly limitedif the ingredient makes it possible to form, on a surface thereof, atitanium nitride layer. Examples of the ingredients are not onlytitanium itself but also titanium alloys, tungsten, iron, organicmaterials which can resist a high temperature of about 200° C. (forexample, an aramid resin and a polyester resin), glass, steel, copper,brass, aluminum, zinc, magnesium, aluminum alloys, zinc alloys,magnesium alloys, lead-silver alloys, high-silicon cast iron, magneticiron oxide, ferrite, artificial graphite, carbon fibers, silicon carbidefibers, and boron fibers. The form of the base material may include anyform, and, for example, a flat plate, a mesh, a foil, a sphere, a cube,a cylinder, a cone, a weaving and a nonwoven.

[0016] In a case where the ingredient of the base material is titanium,a structure having on a surface of the base material a titanium nitridelayer, can be obtained, for example, by evacuating a vacuum heatingfurnace, filling nitrogen gas into the furnace, heating the titaniumbase material up to 800 to 1200° C., preferably 900 to 1100° C. in anatmosphere of nitrogen gas at a pressure of 1×10³ to 1×10⁵ Pa,preferably 1×10⁴ to 1×10⁵ Pa, keeping this temperature for 1 to 60minutes, preferably 30 to 60 minutes, and subsequently naturally-coolingthe resultant in an atmosphere of nitrogen gas in such a manner that thetemperature of the base material will be lowered to a temperature of 100to 300° C.

[0017] In a case where the ingredient of the base material is other thantitanium, any method can be adopted if the method is a method making itpossible to yield a structure having on its base material surface atitanium nitride layer. For example, an ion plating method whereinvacuum evaporation is combined with sputtering can be used. For example,conditions for using the ion plating method are as follows; a substrateis used as the base material, and argon (Ar) gas is introduced into anion plating device, then the device is degassed to have a vacuum of 10⁻⁵to 10⁻³ Torr, and Ar gas sputtering is performed at a substrate appliedvoltage of 350 to 500 V for 15 to 40 minutes, titanium metal is thenevaporated by means of a thermionic gun, then plasma is generated nearelectrodes at an ionization voltage of 30 to 50 V and an ionizationcurrent of 40 to 60 A so as to ionize the evaporated titanium molecules,and a negative voltage is applied to the substrate to form a Ti coat,nitrogen gas is then introduced thereto at an ionization voltage of 45to 70 V and an ionization current of 55 to 75 A. In this way, astructure having on its base material surface a titanium nitride layer,may be obtained.

[0018] Such an ion plating method may not make it possible that alarge-sized base material is plated because the container to beevacuated is limited. Repeatability of conditions is also difficult toperform, so uneven plating and uneven coloration may be generated.

[0019] In a case where the titanium nitride layer is a membrane coveringthe base material, the membrane thickness thereof can be 0.01 to 3 μm,preferably 0.05 to 2 μm, and more preferably 0.1 to 1.0 μm.

[0020] An example of the simple metal which can be used in theelectroplating method is platinum, palladium, gold, silver, copper,zinc, indium, germanium, cobalt, zirconium, tungsten, tantalum, niobium,manganese, molybdenum, tin, iron, aluminum or cadmium. Among thesesimple metals, platinum, palladium, gold and cobalt are preferablebecause of expensiveness thereof. The simple metal layer formed byelectroplating treatment is usually a membrane, and the membranethickness thereof can be set according to the use of the plated product.For example, where a plated product is to be used for a semiconductor,the product comprises a plated gold membrane having a thickness of 5 μmor more, and where a plated product is to be used for an ornament, theproduct generally comprises a plated gold membrane having a thickness of1 to 3 μm.

[0021] An example of the alloy used in the electroplating method is aplatinum alloy, a palladium alloy, a gold alloy, a silver alloy, acopper alloy, a zinc alloy, an indium alloy, a germanium alloy, a cobaltalloy, a zirconium alloy, a tungsten alloy, a tantalum alloy, a niobiumalloy, a manganese alloy, a molybdenum alloy, a tin alloy, an ironalloy, an aluminum alloy, a cadmium alloy, or a blend alloy thereof.Specific examples thereof are Au—Co alloy, Ni—Co alloy, Cu—Zn alloy,Cu—Sn alloy, Au—Cu alloy, Pb—Sn alloy, Sn—Zn alloy, Sn—Cd alloy, Ag—Pballoy, In—Sn alloy, W—Fe alloy, and W—Co alloy or the like.

[0022] Alloy plating is performed in order to improve the functionalityof an object, or to endow an object with functionality. For example, ina case where Ni—Co alloy is applied by plating, results of the platingdiffer if energization conditions differ. If a well-known Weissberg bathis used, an increase in current density causes a Co content in anelectrodeposit to get smaller. In the present invention, as an example,a structure having on its base material surface a titanium nitridelayer, was plated with gold-cobalt.

[0023] The plating bath used in the electroplating method of the presentinvention is not particularly limited if the plating bath is a platingbath making it possible to apply the above-mentioned metal to thetitanium nitride layer by electroplating. Examples of said plating bathsare a sulfuric acid bath, a borofluoride bath, a pyrophosphoric acidbath, a zincate bath, an amine bath, a chloride bath, a cyanide bath, aWatt bath, a sulfamic acid bath, an ordinary bath, a Weissberg bath, asodium bath, a potassium bath, a strike bath and the like. Among theseplating baths, acidic baths such as a sulfuric acid bath are preferablebecause the structure of the present invention can be used therein as ananode instead of a platinum electrode. A neutral bath or an alkali bathmay also be sufficient for the structure of the present invention to beused therein as an anode. Usually, in alkali baths, stainless steel isused as an anode in many cases, and platinum, which is expensive, is notused very much.

[0024] In the method of the present invention, a structure having on itsbase material surface a titanium nitride layer, is used as an electrode;therefore, this electrode can be used as an anode instead of a platinumelectrode and thus the method is inexpensive. Electroplating treatmentcan be applied directly to the titanium nitride layer, so it isunnecessary to use nickel and to worry about nickel allergy. Even ifpretreatment for cleaning the base material surface, such as acidcleaning or degreasing, is not conducted, gold or the like can be stablyand firmly attached to the base material surface by the electroplatingtreatment because the titanium nitride layer has been formed.

[0025] The structure of the present invention can be applied to anyproduct if the product is to be energized. The structure of the presentinvention can be used, for example, in the following products:energization parts such as a plug pin of electric heating articles;various electrodes such as plating electrodes, inner wall electrodes ofan electrolysis cell, electrodes for electrolytic protection, referenceelectrodes, and electrodes for regenerating deteriorated concrete (analkalifying method, a desalting method and so on), and a conductor.

[0026] According to the present invention, an electroplated productobtained by electroplating a structure having on its base materialsurface a titanium nitride layer with a metal such as gold, can be used,for example, in the following products: personal ornaments such as awatch case, a watch band, the frame of a pair of spectacles, and apendant; energization parts such as a plug pin of electric heatingarticles; various electrodes such as plating electrodes, inner wallelectrodes of an electrolysis cell, electrodes for electrolyticprotection, reference electrodes and electrodes for regeneratingdeteriorated concrete (an alkalifying method, a desalting method and soon); machining tools such as a mold; metal dedicated materials forbuilding or construction such as a shutter, a guardrail and a windowframe; and packaging metal containers such as high-pressure gas cylinderand a drum; a dental prosthesis; tableware such as a teapot and a ricebowl; an electrolysis cell; an industrial water tank; a semiconductordevice; and a conductor.

EXAMPLE 1

[0027] A vacuum heating furnace was evacuated, and subsequently nitrogengas was introduced into the furnace to heat a titanium plate (20 cm inlength, 4.5 cm in width, and 1.1 mm in thickness) therein up to 1000° C.at a pressure of 5×10⁴ Pa. This temperature was kept for 30 minutes.Thereafter, the titanium plate was naturally cooled to a temperature of200° C. in an atmosphere of the nitrogen gas so as to yield a platehaving a titanium nitride layer (titanium nitride plate). Since theentire surface of the titanium plate was changed in color to goldencolor, it was proved that the titanium nitride layer was generated. Fourprobes for 150 μm of a resistivity measuring apparatus (manufactured byKyowa Riken Ltd.) were brought into contact with the formed titaniumnitride layer to measure the titanium nitride layer for surfaceresistance.

[0028] The average of the resistances at the three points was 0.059 Ω/□.Since no oxide layer was formed on the titanium plate surface but thetitanium nitride layer was formed thereon, such a low resistance wasobtained.

[0029] Next, a direct current power source device was used to energize aplating bath having the following conditions at a current value of 0.99A for 25 minutes, in which bath platinum to be used as an anode and thetitanium nitride plate to be used as a cathode were immersed. TABLE 1[Plating bath conditions] Potassium auric cyanide 4 g/L (in terms of Au)Cobalt chloride 2 g/L (in terms of Co) HCl 20 ml/L Citric acid 100 g/LLiquid temperature 55° C. pH 1 or less Current density 1 A/dm²

[0030] After the termination of the energization, the titanium nitrideplate used as the cathode was measured for the thickness of a goldmembrane formed thereon. It was found that the gold membrane formed hadan average membrane thickness of 0.829 μm. The voltage at the initiationof the energization was 1.14 V, and the voltage immediately beforetermination of the energization was 2.75 V.

[0031] Next, an adhesive tape was attached to this gold membrane toexamine two times at an interval therebetween whether or not the goldmembrane peeled off. It was proved that the gold membrane adhered firmlyto the titanium nitride plate without peeling off.

EXAMPLE 2

[0032] In the same way as in Example 1, a titanium nitride plate wasyielded. Thereafter, a direct current power source device was used toenergize a plating bath having the same conditions as in Example 1 at acurrent value of 1.00 A for 30 minutes, in which bath the titaniumnitride plate to be used as an anode and a bronze plate for use in theHull cell test method to be used as a cathode were immersed.

[0033] After the termination of the energization, the bronze plate usedas the cathode was measured for the thickness of a gold membrane formedthereon. It was found that the gold membrane formed had a minimumthickness of 2.76 μm and a maximum thickness of 3.6 μm. The voltage atthe initiation of the energization was 2.54 V, and the voltageimmediately before the termination of the energization was 2.6 V. Theliquid was not turbid and the current was stable.

[0034] Next, an adhesive tape was attached to this gold membrane toexamine whether or not the gold membrane peeled off at the points wherethe membrane thickness was 2.76 μm and where 3.6 μm. It was proved thatat both the points the gold membrane adhered firmly to the bronze platewithout peeling off.

[0035] The titanium nitride plate used as the anode was not dirty anddid not dissolve, so it was confirmed that the titanium nitride platefulfilled an electrode function sufficiently.

EXAMPLE 3

[0036] In the same way as in Example 1, a titanium nitride plate wasyielded. Thereafter, a direct current power source device was used toenergize a plating bath having the following conditions at a currentvalue of 0.99 A for 30 minutes, in which bath the titanium nitrideplates to be used both as an anode and a cathode were immersed. TABLE 2[Plating bath conditions] Potassium gold cyanide   6 g/L Sodiumdihydrogenphosphate  15 g/L Dipotassium hydrogenphosphate  20 g/L Nickelpotassium cyanide 0.5 g/L Liquid temperature 70° C. pH 6.5 to 7.5Current density 0.5 A/dm²

[0037] After the termination of the energization, the titanium nitrideplate used as the anode was sound because it was not dirty and did notdissolve. The liquid was not contaminated. The titanium nitride plateused as the cathode was firmly plated with a gold membrane having athickness of about 2.44 μm. The voltage at the initiation of theenergization was 1.9 V, and the voltage immediately before thetermination of the energization was 2.45 V.

COMPARATIVE EXAMPLE 1

[0038] Plating treatment was conducted under the same conditions as inExample 2 except that a titanium plate was used as the anode instead ofthe titanium nitride plate of Example 2.

[0039] In order to turn on the current having a current density of 1A/dm², it was necessary to raise the voltage up to 11-13 V. Thus, powerconsumption increased sharply. This is because an oxide film wasgenerated on the titanium plate surface and the resistance value thereofwas raised.

[0040] It was proved that after the termination of the energization for30 minutes, the titanium plate eluted metal and considerable turbidnesswas generated in the liquid. In a case where only a titanium plate wasused as the anode, the bronze plate of the cathode was able to beelectroplated but the plated surface was largely dirty and unpractical.

[0041] Industrial Applicability

[0042] As described above, according to the present invention astructure having on its base material surface a titanium nitride layer,can be plated; therefore, in a case of plating titanium with gold, saidstructure can be directly plated with gold on the basis of the nitridingof titanium while hitherto titanium is plated with gold after beingplated with nickel, so that according to the present invention theplating process can be made simple and can be reduced in costs.

[0043] A structure having on its base material surface a titaniumnitride layer and having electric conductivity, is resistant tocorrosion and is a good conductor for electricity; therefore, saidstructure can be used as a substitute for a platinum electrode.Moreover, according to the present invention an electroplating methodcan be carried out at a relatively low voltage, and economical effectssuch as a decrease in electric energy and a large reduction in costs canbe achieved.

1. A structure that is endowed with electric conductivity byplate-coating with a titanium nitride layer or by generation of atitanium nitride layer on a surface of a base material made of aninorganic material.
 2. A structure that is endowed with electricconductivity by plate-coating with a titanium nitride layer or bygeneration of a titanium nitride layer on a surface of a base materialmade of an organic material.
 3. The structure according to claim 1,wherein said base material is made of a metal having electricconductivity.
 4. The structure according to claim 3, wherein said basematerial is made of titanium or a titanium alloy, and said structure isobtainable by direct nitriding of the base material surface.
 5. Thestructure according to claim 1, wherein said base material is made of amaterial having no electric conductivity.
 6. The structure according toclaim 1, wherein thickness of the titanium nitride layer is from 0.01 to3 μm.
 7. A method of electroplating a cathode with a simple metal or analloy, wherein an anode comprises a structure that is endowed withelectric conductivity by plate-coating with a titanium nitride layer orby generation of a titanium nitride layer on a surface of a basematerial made of an inorganic material or an organic material.
 8. Amethod of electroplating a cathode with a simple metal or an alloy,wherein the cathode comprises a structure that is endowed with electricconductivity by plate-coating with a titanium nitride layer or bygeneration of a titanium nitride layer on a surface of a base materialmade of an inorganic material or an organic material.
 9. The methodaccording to claim 7, wherein the cathode is plated with a noble metal.10. The method according to claim 8, wherein the cathode is plated witha noble metal.